2. SAC – 101 Fundamentals of Soil Science (Theory)
Credit: 2; Hours/week: 2
Unit 1
Soil as a natural body, Pedological and Edaphological concepts of soil; Soil genesis: soil forming
rocks and minerals; weathering, processes and factors of soil formation; Soil Profile, components of soil;
Unit 2
Soil physical properties: soil-texture, structure, density and porosity, soil colour, consistence and plasticity;
Elementary knowledge of soil taxonomy classification and soils of India; Soil water retention, movement and
availability;
Unit 3
Soil air, composition, gaseous exchange, problem and plant growth, Soil temperature; source, amount and flow of
heat in soil; effect on plant growth, Soil reaction-pH, soil acidity and alkalinity, buffering, effect of pH on nutrient
availability;
Unit 4
Soil colloids - inorganic and organic; silicate clays: constitution and properties; sources of charge; ion exchange,
cation exchange capacity, base saturation; soil organic matter: composition, properties and its influence on soil
properties; humic substances - nature and properties;
Unit 5
Soil organisms: macro and micro organisms, their beneficial and harmful effects; Soil pollution - behaviour of
pesticides and inorganic contaminants, prevention and mitigation of soil pollution.
3. Unit 5
Soil organisms: macro and micro
organisms, their beneficial and harmful
effects;
Soil pollution - behaviour of pesticides
and inorganic contaminants, prevention
and mitigation of soil pollution.
5. Suggested Readings
1. Sharma, N.L. & Singh, T.B. (1996) Soil Science ( Hindi ed.)
Rama pub. House, BarotMerrut ( U.P )
2. Baver, L.D. Gardener, W.H. and gardener W.R.(1976) Soil
Physics Wiley Eastern Ltd, New Delhi
3. Biswas, T.D. and Mukherjee, S.K. (2006) Text book of soil
science.Tata McGraw Hill publishing Co. Ltd, New Delhi
4. Brady, N.C. and Weil, R.R. (2002) The nature and
properties of soils, prentiee hall of India Pvt. Ltd, M-97,
Connaught Circus, New Delhi
5. Das, D.K. (2002) Introductory Soil Science, Kalyani
publisher, New Delhi
6. Rai, M.M. (2002) Principal of Soil Science Mac Millan India
Ltd, New Delhi
7. Mehra R.K. (2004) Text book of Soil Science, ICAR, New
Delhi
6. SOIL ORGANISM
Any organism inhabiting the soil during part or all of its life. Soil organisms, which
range in size from microscopic cells that digest decaying organic material to small
mammals that live primarily on other soil organisms, play an important role in
maintaining fertility, structure, drainage, and aeration of soil. They also break down
plant and animal tissues, releasing stored nutrients and converting them into forms
usable by plants. Some soil organisms are pests. Among the soil organisms that are
pests of crops are nematodes, slugs and snails, beetle larvae, fly larvae, caterpillars,
and root aphids. Some soil organisms cause rots, some release substances
that inhibit plant growth, and others are hosts for organisms that cause animal
diseases.
7. THE BENEFICIAL ROLES OF
SOIL ORGANISMS
Soil organisms benefit plants in a variety of ways such as:
The majority of a plant’s nutrients are derived from beneficial organisms working
in the soil surrounding the plant’s roots; this process is known as the soil food web.
They compete with, inhibit and consume diseases
Soil organisms retain nutrients in the soil, preventing them from leaching
They decompose plant residue, toxic materials and pollutants that kill plant roots
They form soil aggregates that improve water infiltration, root penetration and
water-holding capacity of the soil
Soil organisms aid in a process known as mineralization, which is where nutrients
are broken down and returned to their mineral forms. This allows the plant to take
in the nutrients as needed.
8. THE HARMFUL ROLES OF SOIL
ORGANISMS
Following are some of the harmful roles played by the soil organisms:
Soil organisms tend to Inhabit germination of seed
They lead to immobilisation of plant nutrients
Soil organisms also Inhabit the growth of plants and their development
They cause production of photo-toxic substances
They lead to induction of plant diseases
9. CLASSIFICATION OF SOIL ORGANISM
Soil microorganisms can be classified on the basis of size as follows:
1. Bacteria
2. Actinomycetes
3. Algae
4. Protozoa
5. Fungi
6. Rotifers
7. Mycorrhiza
10. CLASSIFICATION OF SOIL ORGANISM
BACTERIA
Bacteria and Archaea are the smallest organisms in soil apart from viruses. Bacteria
and Archaea are prokaryotic. All of the other microorganisms are eukaryotic, which
means they have a more advanced cell structure with internal organelles and the ability
to reproduce sexually. A prokaryote has a very simple cell structure with no internal
organelles. Bacteria and archaea are the most abundant microorganisms in the soil, and
serve many important purposes, including nitrogen fixation.
ALGAE
Algae can make their own nutrients through photosynthesis. Photosynthesis converts
light energy to chemical energy that can be stored as nutrients. For algae to grow, they
must be exposed to light because photosynthesis requires light, so algae are typically
distributed evenly wherever sunlight and moderate moisture is available. Algae do not
have to be directly exposed to the Sun, but can live below the soil surface given
uniform temperature and moisture conditions. Algae are also capable of performing
nitrogen fixation.
11. CLASSIFICATION OF SOIL ORGANISM
ACTINOMYCETES
Actinomycetes are soil microorganisms. They are a type of bacteria, but they share
some characteristics with fungi that are most likely a result of convergent evolution
due to a common habitat and lifestyle. They can be terrestrial or aquatic. They are of
great economic importance to humans because agriculture and forests depend on their
contributions to soil systems. In soil, they behave much like fungi, helping
to decompose the organic matter of dead organisms so the molecules can be taken up
anew by plants. In this role the colonies often grow extensive mycelia, like a fungus
would, and the name of an important order of the phylum, Actinomycetes (the
actinomycetes), reflects that they were long believed to be fungi. Some soil
actinobacteria (such as Frankia) live symbiotically with the plants whose roots pervade
the soil, fixing nitrogen for the plants in exchange for access to some of the
plant's saccharides.
PROTOZOA
Protozoa are eukaryotic organisms that were some of the first microorganisms to
reproduce sexually, a significant evolutionary step from duplication of spores, like
those that many other soil microorganisms depend on. Protozoa can be split up into
three categories: flagellates, amoebae and ciliates.
12. CLASSIFICATION OF SOIL ORGANISM
FUNGI--Fungi are important in the soil as food sources for other, larger organisms, pathogens,
beneficial symbiotic relationships with plants or other organisms and soil health Fungi can be
split into species based primarily on the size, shape and colour of their reproductive spores,
which are used to reproduce. Most of the environmental factors that influence the growth and
distribution of bacteria and actinomycetes also influence fungi. The quality as well as quantity
of organic matter in the soil has a direct correlation to the growth of fungi, because most fungi
consume organic matter for nutrition. Fungi thrive in acidic environments, while bacteria and
actinomycetes cannot survive in acid, which results in an abundance of fungi in acidic areas.
Fungi also grow well in dry, arid soils because fungi are aerobic, or dependent on oxygen, and
the higher the moisture content in the soil, the less oxygen is present for them.
ROTIFERS--Rotifers can be found in many freshwater environments and in moist soil, where
they inhabit the thin films of water that are formed around soil particles. The habitat of rotifers
may include still water environments, such as lake bottoms, as well as flowing water
environments, such as rivers or streams. Rotifers are also commonly found
on mosses and lichens growing on tree trunks and rocks, in rain gutters and puddles, in soil or
leaf litter, on mushrooms growing near dead trees, in tanks of sewage treatment plants, and
even on freshwater crustaceans and aquatic insect larvae. Because of their very small size and
mostly soft bodies, rotifers are not commonly favoured for fossilization.
13. CLASSIFICATION OF SOIL ORGANISM
MYCORRHIZA
Mycorrhiza defines a (generally) mutually beneficial relationship
between the root of a plant and a fungus that colonizes the plant root. In
many plants, mycorrhiza are fungi that grow inside the plant’s roots, or
on the surfaces of the roots. The plant and the fungus have a mutually
beneficial relationship, where the fungus facilitates water and nutrient
uptake in the plant, and the plant provides food and nutrients created
by photosynthesis to the fungus. This exchange is a significant factor in
nutrient cycles and the ecology, evolution, and physiology of plants.
14. HARMFUL EFFECTS OF SOIL
ORGANISMS TO HIGHER PLANTS
Some soil fauna such as snails and slugs damage and destroy crops. Ants transfer aphids to
certain crops. Some crop roots are infested with nematodes sometimes seriously enough to
affect the growth of these crops adversely.
Bacteria, fungi and actinomycetes cause plant diseases. However, fungi are responsible for
most of the common plant diseases. For example, species of Pythium, Fusarium and
Rhizoctonia are responsible for the “damping off” of seedlings.
Injurious organisms live in the soil for variable periods. Some disappear within a few years if
their host plants are not grown, but some can survive on other hosts. Once a soil is infested, it
is likely to remain so for a long time.
Soil micro-organisms may compete with crops for available nutrients, especially when their
supply is limited. Micro-organisms assimilate appreciable amounts of nitrogen, phosphorus,
potassium and calcium and growth of crops would suffer due to their non-availability.
Competition for trace elements may be even more serious.
If the drainage of the soil is somewhat restricted, the aerobic microorganisms may deplete
the limited oxygen supply of the soil.
Micro-organisms can induce the deficiencies of some nutrients as well as toxicities of some
others.
15. SOIL POLLUTION
Soil pollution refers to anything that causes contamination of soil and degrades the
soil quality.
It occurs when the pollutants causing the pollution reduce the quality of the soil
and convert the soil inhabitable for microorganisms and macro organisms living in
the soil.
Soil contamination or soil pollution can occur either because of human activities or
because of natural processes. However, mostly it is due to human activities.
The soil contamination can occur due to the presence of chemicals such as
pesticides, herbicides, ammonia, petroleum hydrocarbons, lead, nitrate, mercury,
naphthalene, etc in an excess amount.
The primary cause of soil pollution is a lack of awareness in general people. Thus,
due to many different human activities such as overuse of pesticides the soil will
lose its fertility.
16. CAUSES OF SOIL POLLUTION
Soil pollution can be natural or due to human activity. However, it mostly boils down to the
activities of the human that causes the majority of soil pollution such as heavy industries, or
pesticides in agriculture.
Pesticides
They are generally insoluble in water and non-biodegradable. Therefore, these chemicals will not
gradually decompose and keep on accumulating in the soil. Therefore, the concentration of these
chemicals will increase when the transfer of these chemicals take place from lower to higher
trophic level via the food chain. Hence, it will cause many metabolic and physiological disorders
in humans.
Chlorinated Organic toxins
The harmful effect of DDT and other chemicals led to the introduction of less persistent organic
and more-biodegradable substance such as carbamates and organophosphates. However, these
chemicals act as harmful toxins for nerves, hence they are more dangerous to humans.
Herbicides
Slowly, the industries began production of herbicides like sodium arsenite (Na3AsO3), sodium
chlorate (NaClO3), etc. Herbicides can decompose in a span of few months. However, even they
affect the environment and are not environmentally friendly. Even though they are not as harmful
as organo-chlorides but most of the herbicides are toxic. They are known to cause birth defects.
17. CAUSES OF SOIL POLLUTION
Inorganic Fertilizers
Excessive use of inorganic nitrogen fertilizers leads to acidification of soil and
contaminate the agricultural soil also known as agrochemical pollution.
Industrial Pollution
The incorrect way of chemical waste disposal from different types of industries can
cause contamination of soil. Human activities like this have led to acidification of soil.
Inferior Irrigation Practices
Poor irrigation methods increase the soil salinity. Moreover, excess watering, improper
maintenance of canals and irrigation channels, lack of crop rotation and
intensive farming gradually decreases the quality of soil over time and cause
degradation of land.
Solid Waste
Disposal of plastics, cans, and other solid waste falls into the category of soil
pollution. Disposal of electrical goods such as batteries causes an adverse effect on the
soil due to the presence of harmful chemicals.
Urban Activities
Lack of proper waste disposal, regular constructions can cause excessive damage to
the soil due to lack of proper drainage and surface run-off.
18. HEALTH EFFECTS DUE TO SOIL
POLLUTION
Many common soil pollutants are carcinogenic causing humans who are exposed
to these pollutants to be far more likely to develop cancer than those who are not.
Soil pollution can also cause neuromuscular blockage as well as depression of the
central nervous system, headaches, nausea, fatigue, eye irritation and skin
rash. Soil does not need to be highly contaminated to be harmful to
humans. Humans who eat plants or animals that have accumulated large amounts
of soil pollutants may be poisoned, even if the soil itself does not contain enough
pollution to harm human health.
Furthermore, the presence of heavy metals in soil in toxic amounts can cause
irreversible developmental damage in children. Lead and mercury in soil may also
be harmful to human health. Although lead and mercury may be found naturally in
soil, high concentrations of either metal may cause damage to the developing
brains of young children, which in turn may lead to neurological problems.
19. ENVIRONMENTAL EFFECTS
DUE TO SOIL POLLUTION
According to Pollution Issues, soil pollution naturally contributes to air pollution by
releasing volatile compounds into the atmosphere - so the more toxic compounds soil
contains, the greater the air pollution it creates - and can lead to water pollution if toxic
chemicals leach into groundwater or if contaminated runoff or sewage, which can
contain dangerous heavy metals, reaches streams, lakes, or oceans.
Moreover, soil pollution allows great quantities of nitrogen to escape through ammonia
volatilization and denitrification and the decomposition of organic materials in soil can
release sulphur dioxide and other sulphur compounds, causing acid rain.
Furthermore, acidic soils created by the deposition of acidic compounds, such as
sulphur dioxide brought about by the burning of fossil fuels, produce an acidic
environment that harms micro-organisms, which improve the soil structure by breaking
down organic material and aiding in water flow.
Soil pollution may alter plant metabolism and reduce crop yields and cause trees and
plants that may absorb soil contaminants to pass them up the food chain. Soils polluted
by acid rain have an impact on plants by disrupting the soil chemistry and reducing the
plant's ability to take up nutrients and undergo photosynthesis.
20. MEASURES TO CONTROL SOIL
POLLUTION
Reduce Deforestation and Begin Reforestation: Deforestation and soil erosion
are very much interconnected. Soil erosion can occur when there are no trees or
few plants to prevent the top layer of soil from being removed and transported by
forces of nature, such as water and air, which contribute to soil pollution.
Through reforestation efforts and planting new vegetation in areas that are prone to
erosion, soil pollution can be further prevented.
Avoid Intensive Farming Practices, such as over-cropping and over-grazing, as it
leads to flood and soil erosion and further deterioration of the soil layer.
Reduce Your 'Waste Footprint: Waste, such as plastic, non-biodegradable
materials and litter, can accumulate in fertile land, polluting and altering the
chemical and biological properties of soil. According to the Clean Air Council,
almost one-third of the waste in the U.S. comes from packaging - try to purchase
materials with the least amount of packaging and always Reduce, Reuse and
Recycle!.
21. MEASURES TO CONTROL SOIL
POLLUTION
Discover Soil Washing, which uses water to remove contaminants from soils by
“scrubbing” soil to remove and separate the portion of the soil that is most
polluted. Soil washing reduces the amount of soil needing further cleanup and is
typically used along with other methods to clean up the soil as it is usually not
sufficient enough to do the job alone. Soil washing allows the clean-up of polluted
soil in place without having to excavate.
Discover Bioremediation: Use and incite the growth of naturally-occurring
microorganisms to break down contaminants and remediate soil pollution by using
them as a food source during the aerobic processes, which requires the right
temperature, nutrients and amount of oxygen in the soil.
Use Soil Additives, such as lime and organic matter from composting, which can
adjust soil pH to sustainable levels and reduce soil erosion and pollution.
22. ROLE OF SOIL BIOLOGY IN
AGRICULTURE
Decomposing plant residues: The whole process is very dynamic – while some of
the residues are being eaten and fragmented for the first time by the litter
transformers, other residues have already been sequestered by soil microflora, to
be in turn eaten by micro-fauna predators.
The process of converting plant residues into humus is facilitated by enzymes,
either contained within the soil organisms or secreted by either living or dead soil
organisms into the soil matrix. Some of the most common enzymes found in soils
include, protease,lignose, urease and glucosides. Eventually, the residues will have
been processed to the point that they are relatively stable as humus substances.
Carbon cycle: Soil biota play a key role in the carbon cycle whereby these
organisms assimilate carbon (mainly from plant residues) and act as a large carbon
sink as well as providing a substrate carbon source upon their death for other soil
biota higher in the food web. The ability of soil microbes to tie up large quantities
of carbon in these ‘sinks’ is becoming increasingly important in a world where
greenhouse gas emissions are at the forefront of attitudes and policies alike.
23. ROLE OF SOIL BIOLOGY IN
AGRICULTURE
Improved soil structure: Soil biota can have a direct effect on soil structure. Soil
aggregates are clusters of soil particles comprising sand, silt, clay particles, humus
and soil organisms. Aggregation of the soil is important for
maintaining porosity and for stability of surface soils against erosion. The stability
of aggregates is related to the level of soil organic matter and to the activity of soil
organisms. These smaller aggregates may subsequently be bound together into
larger aggregates (>250 µm) through the action of fungal hyphae. Soil biota bi-
products can also have a direct effect on soil structure.
Degrades chemicals inputs: Agricultural pesticides (herbicides, insecticides and
fungicides) are degraded in the soil principally by the action of microorganisms, a
process termed biodegradation, where biodegradation is defined as the breakdown
of a substance to smaller products caused by microorganisms or their enzymes.
The rate at which different pesticides are biodegraded varies widely but generally
degradation is faster in soils with high microbial diversity and activity. Some
pesticides such as DDT have proven to be recalcitrant. Consequently, they remain
in the environment for a very long time and are known to accumulate into food
chains decades after their application to soil.
24. ROLE OF SOIL BIOLOGY IN
AGRICULTURE
Greenhouse gases: Primary industries are significant emitters of greenhouse gases.
Agriculture is the third largest contributor to Victoria's total greenhouse gas emissions.
Therefore, this sector has an important role to play in reducing Victoria’s emissions.
Nitrous oxide emissions are produced by a range of denitrifying bacteria in the soil,
where they convert nitrate into nitrous oxide. These losses are greatest when soils are
warm and waterlogged, and in those with high nitrate contents. Thus, it is important to
apply nitrogen fertilisers only at times, and in quantities and forms, useful to plants as
overuse of fertiliser can drastically increase levels of denitrification.
Regulates nutrient supply: The Nitrogen cycle Soil biology mediates many different
transformations of nitrogen in the entire N cycle. N-mineralisation and nitrification
provide a useable inorganic N source for plant uptake while N fixing bacteria convert
gaseous nitrogen (N2) to a useable form. These processes are fundamental to the cycle
and are of obvious importance in an agroecosystem context. The ability of soil
denitrifies to release nitrogen oxides from the soil also make these microbes important
in the context of greenhouse gas emissions. Nitrification is the biological oxidation (of
ammonia) with oxygen into nitrite followed by the oxidation of these nitrites into
nitrates that can be used by plants.
25. HA’s
QUES ##Describe the prevention and mitigation of soil pollution.
QUES##Define soil pollution and its causes.
